Method for controlling and/or regulating a cooling system of a motor vehicle

ABSTRACT

The present invention provides a method for controlling and/or regulating a cooling system, a desired coolant temperature being determined from a desired component temperature in a desired coolant temperature determination. Energy consumption of a driving engine and a coolant flow may be taken into consideration in the determination of the desired coolant temperature.

FIELD OF THE INVENTION

The present invention relates to a method for controlling and/orregulating a cooling system of a motor vehicle.

BACKGROUND INFORMATION

A cooling system contains a heat source to be cooled, for example adriving engine of a motor vehicle, that is cooled by a coolant via freeor forced convections. The temperature difference from the heat sourcedepends on the heat input and the coolant flow, while the temperature ofthe coolant is determined from the heat input of the heat source, theheat derivation via the cooler located in the circulation, and the heatcapacities of the materials. Vehicle development focuses, for example,on need-based control or regulation of the cooling system with theobjective of reducing energy consumption, decreasing potentiallyoccurring emissions or maintaining emission limit values, and alsoincreasing the comfort level. In this context, critical thermal loadinglimits of components may not be exceeded. A critical temperature is forexample the temperature of the cylinder head of an internal combustionengine used as a driving engine.

Temperature sensors that record the temperatures of components of aninternal combustion engine or other components to be cooled aredescribed, for example, in the engine engineering journal MTZ 62 (2001)1, pages 30 to 35, “A cylinder sealing concept for future internalcombustion engine generations.” The temperature sensors may situated inthe cylinder head gasket.

A method for the optimal control of the cooling performance of aninternal combustion engine of a motor vehicle is further described infrom German Published Patent Application No. 100 35 770.

A regulating structure or a regulating strategy for controlling thecooling system of a motor vehicle based on a desired coolant temperatureis described, for example, in the two German Patent Application Nos. 10163 944.9 and 101 53 943.0.

SUMMARY OF THE INVENTION

The method of the present invention for controlling and/or regulating acooling system provides for a desired coolant temperature to bedetermined as a function of at least one desired component temperature.

The desired coolant temperature relates in this context to a certainlocation in the cooling system. Provided that the cooling systemincludes a driving engine, in particular an internal combustion engine,such a specific location is, for example, the inlet of the coolant intothe driving engine or the outlet of the coolant.

The desired component temperature may be the temperature of a componentof the driving engine or the desired temperature of another componentintegrated in the cooling system. Such a component may be, for example,an electric motor, a generator, or an electronic module cooled by thecoolant. However, the desired component temperature may also be apredefined desired coolant temperature at a predefined location.

The desired component temperature may be defined in a fixed manner or asa function of parameters, for example.

The relationship between the desired component temperature and thedesired coolant temperature determined therefrom may be provided forexample in a fixed manner on the basis of a determined physicalrelationship or in a variable manner as a function of parameters.Instead of the physical relationship, an experimentally determinedrelationship may also be used as a basis. The relationship must ensurethat the determined desired component temperature is maintained and notexceeded via the determined desired coolant temperature.

The cooling system of the motor vehicle may be controlled and/orregulated using the determined desired coolant temperature or a quantityrepresenting the desired coolant temperature. Reference is made in thisconnection to the already cited, German Patent Application Nos. 101 63944.9 and 101 53 943.0.

A method according to the present invention allows the thermal loadinglimit of the component to be closely approached. This may result inadvantages for the energy consumption of a driving engine, in particularof an internal combustion engine. Other savings may be achieved from theneed-compliant design of the cooling system as well as of the componentsto be cooled.

A process control according to a method of the present invention may beaccommodated for example in a control unit (not shown more closely) of adriving engine so that there are no additional costs for electroniccomponents.

An embodiment of the method of the present invention provides for acalculated temperature difference to be used to determine the desiredcoolant temperature from the desired component temperature, thetemperature difference being subtracted from the desired componenttemperature. The temperature difference is to be defined such that thedesired component temperature is maintained and also possibly notexceeded via the resulting desired coolant temperature.

The temperature difference is first dependent on the heat input into thecooling system that is influenced for example by the energy consumptionof a driving engine contained in the cooling system. Therefore, anembodiment of the method of the present invention provides for theenergy consumption of the driving engine to be taken into considerationin the determination of the temperature difference.

The temperature difference is also dependent on the heat transferbetween the coolant and the surroundings, the heat transfer beingparticularly dependent on the coolant flow. Therefore, an advantageousexample embodiment of the method of the present invention provides forthe coolant flow to be taken into consideration in the determination ofthe temperature difference.

A further example embodiment that may be provided in the use of aninternal combustion engine as a driving engine provides for the heatinput from the fuel consumption of the internal combustion engine to bedetermined by being multiplied by a factor. The factor depends on theenergy content of the fuel as well as from the efficiency of theinternal combustion engine in the presently available working point. Thefactor may be stored in a family of characteristics. The factor is aconstant value in a simpler embodiment. In this context, the constantvalue is advantageously determined at least as a function of the fueltype used. As a result, the method of the present invention may be usedin a particularly advantageous manner for a gasoline internal combustionengine as well as for a diesel internal combustion engine. An embodimentprovides for the temperature difference to be determined from a familyof characteristics in which the energy consumption or fuel consumptionand the coolant flow are provided as input quantities.

A further example embodiment of the method of the present inventionprovides for the desired component temperature to be dependent on thepresently available operating point of a driving engine integrated inthe cooling system. The dependence may be stored in a family ofcharacteristics.

A further example embodiment of the method of the present inventionprovides for the determined desired coolant temperature to be correctedas necessary by a correction temperature that is determined by aregulator from the desired component temperature and a measured actualcomponent temperature.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE shows functional blocks for determining a desired coolanttemperature from a desired component temperature.

DETAILED DESCRIPTION

FIG. 1 shows a desired component temperature 10, which is provided by afirst family of characteristics 11. First family of characteristics 11determines desired component temperature 10 from a speed 12 and a torque13 of a driving engine not shown more closely. Desired componenttemperature 10 is supplied to a desired coolant temperaturedetermination 14 and a regulator 15.

Desired coolant temperature determination 14 includes a second family ofcharacteristics 16, which outputs a calculated temperature difference 19as a function of a coolant flow 17 and energy consumption 18. Desiredcoolant temperature determination 14 also includes a first adder 20,which determines a desired coolant temperature 21 from temperaturedifference 19 and desired component temperature 10.

Regulator 15 uses a desired component temperature 10 and a measuredactual component temperature 23 provided by a temperature sensor 22 todetermine a correction temperature 24, which is supplied to a secondadder 25, which provides a corrected desired coolant temperature 26 fromcorrection temperature 24 and desired coolant temperature 21.

An embodiment of the method of the present invention proceeds asfollows:

Desired component temperature 10 corresponds for example with a maximumallowable temperature of a component to be cooled that is integrated ina cooling system, for example, a driving engine component. Such acomponent is for example a cylinder head gasket of an internalcombustion engine. Components situated outside of the driving engine mayalso be provided as components to be cooled. Such components may beelectric motors, generators, or also electronic modules to be cooled.The coolant itself may also be provided as a component to have a certaindesired component temperature 10 at a predefined location in the coolingsystem. Desired component temperature 10 may be defined in a fixedmanner, for example. Alternatively, desired component temperature 10 mayalso be dependent on parameters described further below.

Desired coolant temperature determination 14 is responsible fordetermining desired coolant temperature 21 from desired componenttemperature 10.

The functional relationship between desired component temperature 10 anddesired coolant temperature 21 may be specified in a fixed manner in asimple embodiment. For example, it may be provided for a fixedlyspecified temperature difference between the two temperatures to bedefined such that the setting actual component temperature maintains anddoes not exceed the maximum allowable component temperature. Therelationship may be calculated on the basis of physical relationships orbe experimentally determined. The simple embodiment may be used inparticular for a cooling system operated in a largely stationary mannerin which the heat flows change only minimally with the exception of awarm-up. Desired component temperature 10 is specified as 110° C., forexample. Desired coolant temperature 21 is then set to be 90° C., forexample.

In general, a relationship between a component temperature and thecoolant temperature may be derived in the following manner. Thesimplification is conducted in the following so that staticrelationships are considered. A general equation representing thequotients from the temperature change and time change is used as abasis. In this context, the time-related component temperature change(dT/dt) equals the quotient from the sum of the heat flows (Σ Qs), whichare supplied to or removed from the component, and the product of mass(m) and specific heat capacity (cp).dT/dt=ΣQs/(m*cp).

The actual component temperature remains constant when the sum of theheat flows is exactly equal to zero. Using the known equations for theheat transfer between component and coolant, this condition, solved forthe coolant temperature, yields a relationship between component andcoolant temperature for the stationary case. In general, the coolanttemperature is a function of the introduced heat quantity (waste heat orpower loss of the component), coolant flow 17, and actual componenttemperature 23. For simplification, the basic heat transfer equation istaken as a basis by convention to determine desired coolant temperature21. This basic equation is as follows:Qs=alpha*A*(desired coolant temperature 21−desired component temperature10)

The component temperature then corresponds with desired componenttemperature 10. The heat transfer coefficient alpha is assumed to beconstant for the sake of simplification. Its volume flow dependence, forexample, is neglected in this context. Heat-transferring surface A maybe estimated. Solving for the coolant temperature results in thefollowing relationship:Desired coolant temperature 21=desired component temperature10−Qs/(alpha*A)

Provided that a driving engine is provided as the heat source, the heatinput depends on the energy consumption of the driving engine. Desiredcoolant temperature 21 may then be determined from desired componenttemperature 10 under consideration of energy consumption 18 of thedriving engine.

Provided that the driving engine is an internal combustion engine, theenergy consumption results directly from the fuel consumption. Acorresponding fuel consumption signal is generally available in theengine control.

Different fuel types may be taken into consideration by differentconstants.

The heat balance at the component to be cooled is not only dependent onthe already considered heat flows but also on coolant flow 17.Therefore, the functional relationship between desired componenttemperature 10 and desired coolant temperature 21 is formed as afunction of coolant flow 17 in an advantageous embodiment. A furtherrefinement of this embodiment provides for coolant flow 17 to be takeninto consideration in the provision of temperature difference 19. Therelationship is advantageously stored in second family ofcharacteristics 16, to which coolant flow 17 is supplied as an inputsignal.

According to a further embodiment, a second family of characteristics 16represents the temperature difference 19 as a function of energyconsumption 18 as well as coolant flow 17. For a specified desiredcomponent temperature 10 of 110° C., for example, temperature difference19 is output from second family of characteristics 16 as 20° C., forexample. An increase in energy consumption 18 results in an increase intemperature difference 19 to 30° C., for example, while an increase incoolant flow 17 results in a decrease in temperature difference 19 to10° C., for example.

Another embodiment relates to the provision of desired componenttemperature 10, which may be determined as a function of a working pointof an existing driving engine. Provided that the driving engine is aninternal combustion engine, the working point may be represented forexample by speed 12 and/or torque 13 of the internal combustion engine.

In the depicted exemplary embodiment, speed 12 and torque 13 aresupplied to first family of characteristics 11, which outputs desiredcomponent temperature 12.

An advantageous further refinement provides for the use of regulator 15.Regulator 15 uses desired component temperature 10 and actual componenttemperature 23 to determine correction temperature 24, via which desiredcoolant temperature 21 is corrected in second adder 25 to form correcteddesired coolant temperature 26. Actual component temperature 23 isprovided by temperature sensor 22, which measures the temperature of thecomponent. Regulator 15 includes at least one component that ensuresstationary accuracy. Regulator 15 first corrects a stationary errorunderlying the functional relationship between desired componenttemperature 10 and desired coolant temperature 21 in desired coolanttemperature determination 14. The deviation may be caused, for example,by potentially available second family of characteristics 16, whichoutputs temperature difference 19. In the case of non-stationaryconditions, regulator 15 also supports the downstream control orregulation of the coolant temperature to which corrected desired coolanttemperature 26 is supplied. The upstream regulation supports thedownstream regulation, thereby increasing the overall regulating speedand accuracy.

1. Method, comprising: determining a desired coolant temperature atleast as a function of a desired component temperature; and providing afamily of characteristics; wherein a temperature difference is: derivedfrom the family of characteristics, a coolant flow, and an energyconsumption; and subtracted from the desired component temperature inorder to obtain the desired coolant temperature.
 2. The method of claim1, wherein the desired component temperature depends on an operatingpoint of the driving engine contained in the cooling system.
 3. Themethod of claim 2, wherein the desired component temperature depends onat least one of a speed and a torque of the driving engine.
 4. Method,comprising: determining a desired coolant temperature at least as afunction of a desired component temperature; and providing a regulatorto determine a correction temperature which is used to correct thedesired coolant temperature, the correction temperature being determinedfrom the desired component temperature and an actual componenttemperature measured by a temperature sensor.
 5. A method forcontrolling a cooling system, comprising: determining a desired coolanttemperature at least as a function of a desired component temperature;wherein a coolant flow is taken into consideration in determining thedesired coolant temperature.
 6. A method for controlling a coolingsystem, comprising: determining a desired coolant temperature at leastas a function of a desired component temperature; wherein a heat inputof a driving engine included in the cooling system is taken intoconsideration in determining the desired coolant temperature.
 7. Themethod of claim 6, wherein a temperature difference is subtracted fromthe desired component temperature in order to obtain the desired coolanttemperature.
 8. The method of claim 6, wherein an energy consumption ofthe driving engine is taken into consideration in determining thedesired coolant temperature.